Erase and reinstall Mac OS X Lion

You can erase your computer using Disk Utility and then reinstall Mac OS X. Before you erase and reinstall, back up your essential files. If you’re installing on a portable computer, make sure your power adapter is connected and plugged in.

Important: To reinstall Mac OS X, you need to be connected to the Internet.

  1. Choose Apple menu > Restart, and then hold down the Command (⌘) and R keys while the computer restarts.
  2. Select “Disk Utility,” and then click Continue.
  3. Select your startup disk from the list on the left, and then click the Erase tab.
  4. From the Format pop-up menu, select Mac OS Extended (Journaled), type a name for your disk, and then click Erase.
  5. After the disk has been erased, choose Disk Utility > Quit Disk Utility.
  6. If you’re not connected to the Internet, choose a network from the Wi-Fi menu in the right corner of the menu bar (in the top-right corner of the screen).
  7. Select Reinstall Mac OS X, click Continue, and then follow the instructions.